Transfer process for producing stencils



- written.

United States Patent 3,181,458 TRANSFER PRUiIESS FGR PRODUCDIG STENQILS Max Van Dam, Newton, Omar Baturay, Andover, and Walter C. Zaniewsid, Swartswood, NJ assignors to Anken Chemical & Film Corporation, Newton, NJ. No Drawing. Filed Feb. 16, 1961, Ser. No. 3?,676 5 Claims. (Cl. l01128.3)

This invention relates to stencils for use in duplicating processes and, more particularly, to a new process for producing duplicating stencils.

The present and widely used method for producing stencils for duplicating processes comprises cutting or displacing a relatively soft, ink-impervious coating on an ink-transmissive support of porous paper or cloth. Where the ink-impervious coating has been cut or displaced, the porous paper or cloth permits passage of ink through the stencil onto the surface to be imprinted. The present method of manufacturing duplicating stencils, however, is time consuming since each printing character or letter must be individually cut into the stencil master. Furthermore, it is not possible to produce stencils which are exact facsimiles of the original copy.

Accordingly, it is an object of this invention to provide an improved process for producing duplicating stencil masters.

A further object of this invention is to provide a method for producing duplicating stencils directly from original copies without the application of pressure to cut or displace the stencil coating.

Another object is to provide a process for producing duplicating-stencils which are exact facsimiles of the original copy.

Still another object is to provide a process for producing a number of duplicating stencils from the same original copy, all of which stencils being facsimile duplicates of the original copy.

A still further object is to produce facsimile duplicating stencils by simplified and convenient photographic techniques.

In accordance with this invention, a stencil having ink-transmitting openings which are facsimile duplicates of the indicia of an original copy, is produced by exposing a photographic silver halide emulsion coating to an indiciated original copy, developing the exposed emulsion coating in contact with a heat-fusible coating on a stencil tissue with a photographic developer solution containing silver nucleating agent and in the presence of a silver halide solvent, to produce a silver image copy of the original indicia on the stencil coating. The developed silver halide emulsion coating and the stencil sheet are then separated, and the imaged stencil coating is placed in w. /contact with an absorbing surface, and heat-generating radiation is directed through the stencil coating whereby the radiation absorbed by the silver images causes the stencil coating coextensive with the silver images to liquefy and be absorbed by the adjacent absorbing surface.

Ofiice copying equipment now in wide use offers readily available and convenient means for preparing duplicating stencils by the present invention from existing documents, letters and the like, whether printed, typed or hand- Thus the steps of exposing photographic coating to an existing copy desired to be duplicated, and the transfer processing of the exposed coating in contact with the stencil coating, are advantageously performed in any one of a number of well known, Widely used oflice copying machines of the diffusion transfer type. The remaining step of the present process, namely, liquefying the stencil coating coextensively with the silver images developed thereon, may be readily carried out in another type of oifice copying machine wherein the light source is rich in infra-red or heat generating radiation.

illAE Patented R ley 4, 1965 The practice of this invention is facilitated by providing stencil tissue paper or cloth supports with a coating composition which is non-tacky and solid at normal room temperature but which can be melted or converted to the liquid state at temperatures substantially above normal room temperature. Preferably, the melting point of the stencil coating is in the range of from C. to C., but stencil coatings useful in the present process may have a melting point as high as 260 C. or even higher, because the stencil coatings as used herein are substantially transparent to the heat-generating radiation except in the silver image areas.

In the manufacture of stencil blanks for use in the present image transfer process, the porous support is coated with a continuous layer of heat-fusible composition comprising natural or synthetic Waxes or wax-like materials capable of being reduced to the liquid state by the application of heat. In addition, such coating compositions may also contain plasticizers and, preferably, sur face-active agents for increasing receptivity ofthe waxlike coatings to the aqueous processing solution. Additionally, the stencil coating compositions may also contain other fusible, film-forming bodying agents such as cellulose ethers and esters.

As used in the process of this invention, the stencil coatings serve not only the ultimate purpose of modulating the flow of liquid marking compositions, but also as the reception coatings in photographic diffusion transfer processes and as heat-sensitive coatings in thermal printing processes, as hereinafter described. Accordingly, the melting point of the'stencil coating is but one criterion in the formulation and coating of such compositions. Additionally, one surface of the stencil coating should be of mirror-like smoothness to insure maximum, intimate contact of the stencil coating surface with the surface of the exposed silver halide emulsion coating during the diffusion transfer processing step. The necessary mirrorlike or glossy surface can be produced on the stencil coating surface by causing the surface to flow under pressure into conformity with the surface of, for example, photographic film base or the highly polished surfaces of chromium plated ferrotype plates or ferrotyping drums such as are used for producing high gloss on photographic prints. lossing or ferrotyping of the stencil coating surface may be performed at any time before the photographic diffusion transfer'step and is conveniently done immediately after the coating is applied and before the coating composition has completely solidified.

The stencil support or reinforcement base may be of open-texture, porous, Japanese bibulous paper prepared with Yoshino fibers or other similarly textured porous papers formed of natural fibers such as, for example, vegetable fibers of the Musa family or genus, particularly fibers of the banana species, such stencil base papers being described in Patent No. 2,045,096. For stencil coatlogs with higher melting points, with resultant higher stencil life, open texture papers formed of synthetic fibers such as spun glass fibers, fibers formed of mineral wool, and asbestos are particularly advantageous. For graphic arts use, such as in the silk screen printing field, the stencil support may be of the well known silk bolting cloth or similar bolting cloths woven with synthetic fibers such as polyamide or polyester fibers.

The fibrous support or reinforcement web is coated or impregnated with the heat-displaceable composition by, for example, the hot-melt method whereby a continuous solid film of the coating composition is formed on the web upon cooling of the coating. The film coating may also be formed by evaporation, at room or elevated temperature, of a solvent or diluent contained in the coating composition, said coating being applied by spray-coating, or by other coating procedures Well known in the art.

xuos film not only covering the individual fibers of the structure of the web but also filling the interstices between the fibers.

In the practice 'of applying the coating to the web support, the thickness of the coated film, expressed as such or in terms of coating weight, may 'be varied depending upon the characteristics of the coating composition, such as melting point, desired printing life, duplicating capacity of the stencil master, and others. In general, however, a coating thickness of about 4 mils has been found to be satisfactory for a readily fusible. stencil coating. For stencil coatings having a higher melting point, the coating thickness may be considerably less, in order of 1 to 2 mils.

In preparing duplicating stencil masters by the present process, a silver halide emulsion coated on a paper or film support is exposed to an original copy, such as a typewritten letter. The latent photographic image is then developed by the image diffusion transfer process, while the exposed emulsion coating is pressed into intimate contact with the glazed surface of the stencil coating. In such diffusion transfer processes, unexposed silver halides are dissolved by a silver halide solvent in the processing solution and are transferred by diffusion to the surface of the stencil coating where the silver salts are reduced by the developing solution to form a silver image duplicate of the original copy. As heretofore widely practiced in the diffusion transfer process, the diffused silver salts are reduced to metallic silver on, and partly in, a reception coating comprising, generally, a layer of a water-sensitive colloid such as gelatin, casein or polyvinyl alc-ohol'or mixtures thereof. Such water-sensitive reception coatings contain nucleating agents which serve to catalyze the reduction of the silver salts and accelerate the development of the silver images on the reception coatings. The coat ings are maintained in contact with each other from to 60 seconds to form a developed silver image on the reception layer and then the coated surfaces are stripped apart revealing the silver'image copy of the original on the reception coating.

Nucleating agents for catalyzing reduction of silver ions and accelerating the development of the transferred silver salts are also known as fogging agents, since they render the silver halides of photographic emulsions developable in the absence of light. Such fogging or nucleating agents comprise physical development nuclei and chemical pre'cipitants for silver ions and include colloidal silver, colloidal silver sulfide, colloidal silver protein complexes such as mild silver protein, zinc sulfide, cadmium sulfide, organic sulfiding agents such as mercaptates, xanthates, thiourea and thiourea derivatives such as allyl thiourea which react with the dissolved silver halide complex salts to form colloidal silver sulfide; and reducing agents such as sodium stannite and substituted hydrazines which form colloidal silver with a portion of the dissolved silver salts.

In the present application of the diffusion transfer process, the hydrophobic, heatasensitive stencil coating serves as the reception coating for the transferred silver ions and the nucleating agent is present in the processing solution instead of being a component of the reception coating. It has been found, surprisingly, that water-soluble nucleating agents, such as, for example, silver gelatin'ate and mild silver protein serve efficaciously in accelerating the reduction of transferred silver ions and the formation of silver images on water-insensitive stencil coatings. Patent No. 2,657,618, issued to Walter Eisbein on Novemher 3, 1953, discloses a machine suitable for performing the diffusion transfer process hereinabove described, and the drawing of said patent is herein incorporated by reference. There .are presently on the market diffusion transfer process machines for making office copies, such as the Ampto 12 and the Ampto 14 sold by Ampto, Inc., of Newton, New Jersey, which are admirably suited for both exposing the photographic emulsion coated paper to the original copy and for the transfer processing for imaging the stencil coating surface with a silver image copy of the original.

In addition to having a nucleating agent present in the transfer processing solution, it has been found that the the presence of a small amount of a hydrophilic, filmforming protective colloid is advantageous for producing silver images which have a high absorption characteristic for heat-generating radiation. Such film-forming protective colloids are provided, for example, by polypeptide-containing silver complexes such as silver gelatinate and silver nucleate or mild silver protein. For other nucleating agents, the protective colloid is added as to the processing as an individual compound and may be selected from a number of hydrophilic, water-dispersible, film-forming colloids such as, for example, methyl cellulose, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol and partially hydrolyzed polyvinyl acetate-boric acid complexes. The presence of such protective colloids in the transfer processing solution appears to result in the formation on the stencil coat ing of silver images which have dense, closely-packed silver grains rather than the filamentary or fibrous type of silver grains.

The coated stencil'blank, bearing a silver image copy of an original developed on and partly in the polished surface of the coating, is then exposed to radiant energy of wave lengths which are absorbed by the silver images and, concomitantly, raise the temperature thereof. During the exposure to the heat-generating radiation, at least the image surface of the stencil coating is held in intimate contact with an absorbent for the stencil coating composition in the liquid state. Suitable absorbents are white blotting paper or ordinary newsprint paper. Several layers of uncoated stencil base paper serve advantageously as an absorbent, and this has the additional advantage of allowing the heat-generating exposure to be made through the absorbent element on to the imaged stencil coating. Where the absorbing element is resistant to the passage of the heat-generating radiation, or opaque thereto, theexposure is made through the unglazed, un'imaged surface of the stencil coating. Because the stencil base or reinforcement is actually imbedded within the coating, both the imaged and the un-imaged surfaces of the coating may be contacted with absorbent sheets during the heatgenerating exposure, thus producing extremely sharpedged, well defined stencil openings.

Since the silver images formed on the stencil coating are efiicient absorbents of heat-generating radiation, such as infra-red radiation, compared with the coating compositions, the thermal radiation exposure need be only long enough and to such range of wave lengths as will elevate the temperature of the silver images to the melting point of the stencil coating, whereupon the coating is reduced to the liquid state coextensively with the silver images. The necessary thermal radiation exposure can be provided, for example, by the radiant emission of ordinary photographic flash bulbs, in which case a number of bulbs must be fired simultaneously to produce sufficient heat-generating radiation. Efiicient, rapid thermal radiation exposure, however, is readily provided by the ordinary incandescent infra-red drying lamps and by other tungsten fila ment lamps operated at higher than rated current densities. Office copying machines which utilize thermographically sensitized copying papers serve admirably for exposing the present silver imaged stencils to thermal radiation. Patent No. 2,740,895, issued to Carl S. Miller on April 3, 1956, discloses a thermoprinting machine which may be used for the purpose last above described, and the drawing of said patent is herein incorporated by reference. Thermographic copying machines sold under the name of Thermofax by the Minnesota Mining and Manufacturing Company and the Master-fax duplicator sold by Ditto,

U Incorporated, are examples of thermal exposing machines useful in the present process.

The following specific examples will further illustrate but are not intended to limit the invention:

Example I Example II Stencil base tissue was. embedded within a film 3.5 mils thick of paraffin wax having a melting point ranging between 240 C. and 260 C. by towing the tissue through a bath of the molten wax. Before the coating had cooled to room temperature, the impregnated tissue was squeegeed into contact with a chromium plated ferrotype plate and allowed to cool and set in contact therewith. When cooled to room temperature, the stencil blank was stripped from the ferrotype plate and the polished surface of the stencil blank was used as a reception surface in the transfer process hereinabove described, and hereinafter illustrated.

I Example 111 To 90 grams of melted stearic acid were added grams of Tergiol Nonionic NP-27 1 and mixed with the acid. Stencil tissue was imbedded in a continuous film 2 mils thick obtained by towing the tissue through the molten mixture and allowing the tissue reinforced film to cool with one surface thereof in contact with a sheet of photographic film base.

Example IV A sheet of stencil tissue was completely covered with a coating prepared by melting 95 grams of Paraffin Wax Sunoco 5512 2 and mixing therewith 5 grams of triethylene glycol di(2-ethylbutyrate) and one surface thereof was glazed as described in Example I.

Example V In addition to the foregoing hot-melt stencil coating compositions, the following compositions were also used to coat stencil tissues which were then allowed to dry, by evaporation of the solvent, with one coated surface in contact with a ferro-type print glazing plate:

8 Baker Castor Oil Company.

Example VI Stencil tissues were also coated with an aqueous dispersion of a wax and stearic acid and containing a stabilizing agent according to the following formula:

Grams Multiwax ML445 b 60 Stearic acid 24 Triethanolamine 7 Water 109 b L. Souneborn Sons, Inc.

1 Nonyl phenyl polyethylene glycol ether, containing 7 mole of ethylene oxide. Union Carbide Chemicals Company.

2 Sun Oil Company.

and dried in contact with a polished surface as described above.

Other stencil tissues were coated with the following stabilized aqueous dispersion of wax and stearic acid:

Grams Parafiin wax, Sunoco 3425 c 60 Sorbitan monopalmitate 6 Tween 40 d 6 Stearic acid 1 Water 127 c Sun Oil Company. d Polyoxyethylene derivative of sorbitan monopalmitnte. Atlas Powder Company.

and then air dried while sandwiched between sheets of polystyrene film base and blotting paper;

Example VII A typewritten letter was printed by reflex exposure onto a high contrast gelatino silver chloride emulsion coating of photographic printing paper. The exposed photographic paper was then wetted with a transfer developer processing solution of the following composition:

Sodium sulfite, anhydrous grams Hydroquinone do 13.5 Sodium hydroxide do 9.0 1-phenyl-3-pyrazolidone do 1.6 Sodium thiosulfate, anhydrous do 10.0 Potassium bromide do- 0.6 1-phenyl-S-mercaptotetrazole do 0.1 Silver gelatinate, 1% solution mls 500 Water to 1 liter.

and immediately pressed into contact with the polished surface of a stencil blank prepared as in Example I. After remaining in contact for 6 seconds, the photographic paper negative was stripped from the stencil blank revealing a dense silver image copy of the original typewritten letter on the stencil coating. The silver imaged surface of the stencil blank was then placed in contact with a sheet of newsprint paper and the sandwiched sheets were exposed through the unpolished surface of the stencil coating in a thermal printer having a radiation emitting source which is high in infra-red radiation. After exposing, the absorbent sheet of newsprint was separated from the thermally exposed stencil blank which now had sharp-imageopenings corresponding to the typed indicia of the typewritten original.

Example VIII The procedure described in Example VII was repeated, using, however, a stencil blank prepared as described in Example 11 and substituting 0.25 gram of mild silver protein for the silver gelatinate solution in the transfer processing solution. The silver imaged stencil blank was sandwiched between sheets of newsprint paper and a thermal radiation exposure was made through the absorbent sheet adjacent the imaged surface of the stencil blank with a General Electric quartz heat lamp Type No. 1350T3CL operated at 280 volts. Upon separating the absorbent sheets, a stencil master having sharp edged, inktransmitting openings, corresponding to the typed characters on the original copy, was obtained.

Example IX A sharp, clear printing stencil master was prepared, using a stencil blank prepared as described in Example 111 and a transfer processing solution of the following Water to 1 liter.

Several thicknesses of uncoated Yoshino fibe'r tissue paper were used as the absorbing medium for the liquefied coating in making the heat-generating exposure through the tissue ab'sor'bjent.

From the foregoing description and the specific examples of the present invention, it is apparent that the addition of silver nucleating agents to the transfer process developing solution enables a silver image duplicate of an original copy to be reproduced on, and to some extent in, a waxy, hydrophobic, ink-impervious stencil blank coating. Such developed silver images, comprising deposits of minute patri'cles of metallic silver, have a high absorption or stopping-power for incident radiation of long wave lengths and dissipate the absorbed energy in the form of heat. Thus the developed silver images on and in the stencil coatings serve as heat-generating image patterns for reducing the stencil coating to a liquid state coextensively with the silver images.

From the foregoing description it is also apparent that the present invention provides means for producing duplic'ating stencils having ink-transmitting openings which are facsimile duplicates of .the indicia characters on an original copy, even to duplicating the style and design of the type used to indicate the original copy. Likewise, the individual characteristic s of handwriting, art designs and patterns, border and decorative effects on original copies are also readily duplicated with stencils prepared as herein described. A further advantage is that addition a1 printing characters may be cut into the stencil after it has been prepared by the process, should additions be found necessary. Moreover, the stencil correction fluids and techniques used to make corrections on ordinary stencil-s may also be used with stencils prepared as herein described. 7

Having thus disclosed the invention, and as many wide 1y different embodiments thereof can be made without departing from the spirit and scope thereof, it'is to be understood that the invention is not to be limited except as defined the following claims.

What is claimed is:

1 The process for producing a duplicating master from an original copy which comprises exposing a silver halide emulsion coating to the copy, developing the exposed emulsion in contact with a heat fusible coating on a stencil with a developing solution containing a silver halide solvent and a nucleating agent whereby a silver image is formed on said coating separating the developed emulsion coating from the stencil coating and exposing the imaged stencil coating to heat generating radiation to liquefy the stencil coating coextensively with the developed images.

2. The process for producing a duplicating stencil master from an original copy which comprises exposing a light sensitive silver halide emulsion coating to the copy, developing the exposed emulsion in contact with a heat fusible coating on a stencil and in the presence of a silver halide solvent, with a developing solution containing a nucleating agent whereby a silver image is formed on said coating, separating the developed emulsion coating from the stencil coating and exposing the silver imaged 8 stencil coating to infrared radiation to elevate the temperature of the silver images and liquefy the stencil coating coextensively with the developed images.

3. The process for producing a duplicating stencil master from an original copy, which comprises exposing a light sensitive silver halide emulsion coating to the copy, developing the exposed emulsion in contact with the glazed surface of a heat fusible coating on a stencil and in the presence of a silver halide solvent, with a developing solution containing a nucleating agent and a film-forming protective colloid whereby a silver image is formed on said coating, separating the developed emulsion from the stencil coating and exposing the silver imaged stencil coating to infra-red radiation to heat the silver images and liquefy the stencil coating coextensively with the silver images. 7

4. A process for producing from an original copy a duplicating stencil master having ink-tnansmitting openings, which comprises exposing a light sensitive silver halide emulsion coating to (the copy, developing the exposed emulsion in contact with the glazed surface of a heat fusible coating on a stencil and in the presence of a silver halide solvent, with a developing solution containing "a silver nucleating agent and a film-forming protective colloid whereby a silver image is formed on said coating, separating the developed emulsion from the stencil coating, exposing the silver imaged stencil coating to infra-red radiation to heat the silver images and liquefy the stencil coating coextensively with the silver images, and removing the liquefied coating and the silver images with a removable absorbent layer.

5. A method of making a duplicating stencil master, comprising the steps of exposing an original to a silver halide coating of a negative to provide a latent image of unreacted silver halide in the unexposed portions of the negative, developing the negative, while in surface contact with a stencil sheet having a heat fusible coating, with a developing solution containing a solvent for the silver halide remaining in the unexposed portions of the negative to cause transfer by diffusion from the negative to the stencil coating in order to form a silver image duplicate on said stencil coating of said original, separating the negative from the stencil sheet, and finally heating said silver image to melt said stencil coating coextensively with said image.

References Cited by the'Examiner UNITED STATES PATENTS 1,973,151 9/34 Murphy 101-1282 2,352,014 6/44 Rott 9629 2,503,758 4/50 Murray.

2,558,857 7/51 Land -a 9629 2,808,777 10/57 Roshkind 10'1-128.2 2,868,124 1/59 Crawford 101401.1 2,969,014 1/61 Hanson et al 101l28.3

WILLIAM B. PENN, Primary Examiner.

ROBERT A. LEIGHEY, ROBERT E. PULFREY,

Examiners. 

1. THE PROCESS FOR PRODUCING A DUPLICATING MASTER FROM AN ORIGINAL COPY WHICH COMPRISES EXPOSING A SILVER HALIDE EMULSION COATING TO THE COPY, DEVELOPINF THE EXPOSED EMULSION IN CONTACT WITH A HEAT FUSIBLE COATING ON A STENCIL WITH A DEVELOPING SOLUTION CONTAINING A SILVER HALIDE SOLVENT AND A NUCLEATING AGENT WHEREBY A SILVER IMAGE IS FORMED ON SAID COATING SEPARATING THE DEVELOPED EMULSION COATING FROM THE STENCIL COATING AND EXPOSING THE IMAGED STENCIL COATING TO HEAT GENERATING RADIATION TO LIQUEFY THE STENCIL COATING COEXTENSIVELY WITH THE DEVELOPED IMAGES. 